The international investigation into the causes of the crash of the Polish presidential plane is probing into a possible lack of pilot training and the presence of non-crew members in the cabin prior to the landing.

The cockpit flight recorder captured the voices of two people who were in the cabin during the flight, but were not members of the crew. One of them has been identified, and the analysis of the second one will be finished soon, Taniana Anodina, chair of the Interstate Aviation Committee (IAC), told journalists. The IAC is a regional executive body investigating the accident.

“The possible influence of [these people] on the crew and their decision-making is subject to further research,” she said.

Anodina refrained from disclosing the name of the identified person.

One of the non-crew members was in the cabin seconds before the moment of the crash, the investigation established.

The situation did not violate Polish flight regulations, Edmund Klich, head of Poland’s Air Incident Investigation commented. The presidential flight was not a civilian aircraft, where intrusion of strangers into pilot cabin is strictly forbidden.

“Polish regulations don’t subject military aviation to these procedures. They are obligatory for all civilian planes, but have not authority over military aviation,” he said.

Another avenue of enquiry for the international investigation is a possible lack of experience among the flight crew.

Chair of the IAC’s investigative commission, Aleksey Morozov, said proximity sensors gave a warning 18 seconds before the impact. The pilots should have responded by effecting an emergency climb.

“I have no answer to why this was not done,” Morozov said.

He added that the pilots had not done regular simulator training for a Tu-154, and that the crew had been formed just a few days before the flight.

Edmund Klich said the military base at which the pilots were stationed had no simulator for this model, and that the Polish Air Force has no standing training program for Tu-154s. Civilian pilots certified for Tu-154 pass such training every six months.

Klich said this issue is now under further investigation and called for a systematic approach. He said several air incidents involving Polish aircraft had been previously linked to violations of regulations by crews.

Theories about terrorism, explosions, and technical difficulties have been ruled out.

Further, the engines are said to have been in good working order prior to the plane crash.

Currently, all documents relating to the investigation are in a safe at the lab where the wreckage of the jet is.

“All of the information has been deciphered and is now being analyzed,” said Viktor Trusov from the Interstate Aviation Committee.

Both Polish and Russian experts are working round the clock to wrap up the investigation and answer all questions about the tragic deaths of Poland's political elite.